1. Field of the Invention
The present invention is directed to methods for inspecting voltage contrast images of integrated circuit dies. More specifically, but without limitation thereto, the present invention is directed to generating simulated voltage contrast images that may be compared to actual voltage contrast images to detect the location and type of defect in an integrated circuit die for a selected test condition.
2. Description of the Prior Art
Voltage contrast imaging is typically performed by directing a beam of charged particles such as ions or electrons onto the surface of an integrated circuit die under test and measuring the number of ions or electrons that are scattered from a net in a selected area in a selected metal layer of the die. If the net has a DC electrical path to the circuit ground, that is, the die substrate, then more ions or electrons are scattered from the net than if the net does not have a DC electrical path to the die substrate. The number of charged particles received by a detector from each pixel of the selected area may be displayed as a brightness level in an image, called a voltage contrast image, that shows in real time whether each net has a DC electrical path to the die substrate. The voltage contrast image may be generated without disturbing the operation of the circuit and without exposing the die to possible damage from mechanical probes.